The consumption of cut flowers such as chrysanthemum, rose, carnation, etc., is increasing year by year, and competition grows more and more keen in production and sales internationally or among domestic producing districts in recent years. Under the circumstances, the development in techniques of maintaining freshness for cut flowers, e.g. of long-lasting of flowers and helping flowers draw water, becomes increasingly important, and such demands are expected to be dissolved by a freshness-keeping agent for cut flowers.
A freshness-retentive for cut flowers (referred to as "retentive," hereinafter) consists of a pre-treatment agent and a post-treatment agent, each with different components and functions. The pre-treatment agent is employed for brief treatment of cut flowers before shipping to a retail shop in order to prolong preservation of flowers after being harvested and help flowers raise water, of which an anion complex of silver thiosulfate containing as a stabilizer a sulfite or the like is widely used at present (Japanese Patent Publication No. 23,521/90). The post-treatment agent comprises, as principal components, nutrients required for flowers (sugars, nitrogen, phosphoric acid, potassium, etc.), a germicide, a surface-active agent, etc., and this agent is to help prolong preservation for flowers on sale in a retail shop or flowers put in a vase for consumer's appreciation. The freshness retentive of the present invention belongs to the pre-treatment agent, but may also be employed as a post-treatment agent.
A wide variety of pharmaceutical agents have been available up to now as pre-treatment agents, among which the above-mentioned anion complex of silver thiosulfate is widely employed at present. Silver ions inhibit the action of ethylene, a plant hormone being influential as a factor of the aging (withering) of flowers. Spraying of carnation with silver nitrate prolongs the freshness of the flower. However, the speed of silver ions, if silver nitrate is absorbed through stems, is very slow in vessels and thus silver ions are difficult to reach the tissues of flower and leaf (Halevy, A. H. and Kofranek, A. M. (1977),"Silver treatment of carnation flowers for reducing ethylene damage and extending longevity." J. Amer. Soc. Hort. Sci., 102, 76-77). H. Veen, a Dutch scientist, prepared an anion complex of silver thiosulfate (Ag(S.sub.2 O.sub.3).sub.2 !.sup.3- complex which is referred to as "silver thiosulfate complex," hereinafter) by mixing silver nitrate and sodium thiosulfate, in order to examine how the silver thiosulfate complex moved in the vessels of carnation. As a result, he found that the silver thiosulfate complex could move very rapidly in the vessels of carnation and prolong preservation of the flower to a great extent (Veen, H. and van de Geijn, S. C. (1978), "Mobility and ionic form of silver as related to longevity of cut carnations." Planta, 140, 93-96, Veen, H. (1977),"Effect of silver on ethylene synthesis and action in cut carnation."Planta, 145, 467-470). The silver thiosulfate complex is presently consumed in a great deal in all over the world because this complex, being capable of production at a low cost, exhibits a strong effect on retaining the freshness of cut flowers.
The silver thiosulfate complex widely used as described above, however, presents the following problems: (1) Silver is a heavy metal, so anxiety over environmental pollution is raised and (2) the silver thiosulfate complex does not have any effect on flowers low sensitive to ethylene, such as chrysanthemum, rose, orchid, etc., although the complex has a freshness retaining effect on flowers highly sensitive to ethylene, such as carnation, Gypsophila elegans, sweet pea, delphinium, etc. Particularly with respect to rose, no effective freshness retentive has been obtained still yet in spite of extensive investigations by researchers in all over the world.